Method of making fin tubing



Feb. 26, 1935. E.-A. DEWALD 1,992,297

METHOD OF MAKING FIN TUBING Original Filed March 6, 1935 2 Sheets-Sheet l INVENTOR W4. BY AM @M WM H/J ATTORNEYS Feb. '26, 1935. E. A. DEWALD 1,992,297

7 METHOD OF MAKING FIN TUBING Original Filed March 6, 1933 2 Sheets-Sheet 2 INVENTOR heres to portions of o protrusions'or knurl marks on the tube surface metal bond of solder Patented set.- 2c, 1935 UNITED STATES PATENT OFFICE .Orlglnal application March andthiaabplioati 0, i933, Ne.-

on Deeem ber 19, 1933, Serial No. 703,062 7 9 Claims. (Cl. 29l5'I-3) This invention relates to fin tubing and more particularly concerns a novel method of'producing fin tubing of an improved construction.

Fin tubing of the type concerned hereinjcomprises a metallic tube having secured to the external surface thereof a thin ribbon-like metallic fin in the form of a helix. Fin tubing ofthis nature is extensively used in the manufacture of heat exchangers.

In the past, fin tubing of the character de-: scribed his been made in either one. of two different ways. Thus, the ribbon or strip of metallic fin material has been wound helically on a tube and then secured thereto by amolten or the like. It has also been the practice to cut a helical groove on the outer surface of the tube, insert the inner edge of a helicahfinin such groove and press the edges of the groove into clamping relation with the fin edge so inserted whereby the fin is secured to the tube. These known methods of attaching helical fins to tubes are unsatisfactory for various reasons. Thus, the soldered constructions are relatively expensive to manufacture and entail considerable loss of soldering material which adthe tube and fin where it is not needed. The grooving method of fin attachment, although satisfactory for certain types of work, cannot be used with success when the tube'walls arethin, because the grooving considerably weakens thetu The present invention has for its object, the provision of a new and improved method of securing a helical fin to a tube. v n

, The present application is a division of my co pending application, serial Number 659,892, filed March 6, 1933, in which the improved tubing, produced by the method of the present invention is-described and claimed. Accordingto the present invention, the outer surface of the tube is first roughened to produce a plurality of teeth, knurl marks or other surface extensions or irregularities which prefer-' ably form ridge-like protrusions extending in a direction generally longitudinally of the tube. The ribbon or fin is then tightly wound edgewise onthe tube and its inner edge. is pressed against the tubesurface with sufiicient force to cause the to embed themselves-into ,the inner edge surface of the fin. when sov wound, it is found that the. engagement of the. tube surface protrusions or knurl'marks with the fin edge is sufficient to effectively prevent theslipping-of the ii.n.a.roui id the tube surface and a highly eiilcient finned tube construction is thereby produced.

It-has been discovered that a highly effective heat conductive bond may be secured between a tube and a helical fin if coiled edgewise about the present invention venting such tightly wrapped fin'from unwinding or otherwise 1 g after it has been coiled on the tube, and this without the use of solder or similar expedients flu in the tube surface or otherwise weakening the the-tube structure.

the tube. The method of A feature of the present invention comprises that the stretch or jacent the limit while the portion of the fin metal adjacent the inner edge'thereof, against the tube surface, is compressed, but notrbe 0nd its elastic limit. With this procedure, the er elastically compressed portion of the fin exerts a considerable force on the tube surface and so maintains the fin firmly in place on the tube, this expansive force being exerted between the tube surface and the set outer. portion of the fin metal which has been stretched beyond its elastic limit and. so maintains the coiled formation of the expansive force.

The helical fin'may be precoiled beforeattach ment of the fin may be effected in a single continuous operation. Also, the surface protrusions or knurl marks may be formed on the tube before or almultaneously with the winding operation.

The invention will be best understood by referwinding operation serves to extend a portion of the fin metal adence to the accompanying drawings in which cere ta'in embodiments thereof have been illustrated; In the drawings;

Pig. 1 is an elevation of a section of knurled tubing to which a, portion of a precoiledhelical fin has been attached in accordance with the invention; a

Fig. 2 is a perspective view of a tube showing one method of forming surface 'protrusionsor knurl marks thereon; v

Fig. 3 is an end elevation of a finned tube in the course of construction in accordance with one embodiment of the invention;

Fig. 4 is a sectional view, taken alongth'e line 4-4 of Fig.3 and viewed in the direction of the arrows;

' Fig. 5 is a sectional view, taken along the line of the, fin in spite to the tiibe'or the coiling and attachment the fin em t h ly 6 provides a means for prej outer edge thereof beyond itselastie;

10 and without embedding the 5-5 of Fig. 3 and viewed in the direction of the arrows; and

6 is an end elevation of a finned tube in' the course of construction in accordance with an other embodiment of the invention.

In a preferred embodiment of the invention,

as best shown in Figs. 3 and4, a metallic tube 5 is'simultaneously provided with external longitudinally extending protrusions or knurl marks 6 and a precoiled metallic fin or ribbon '7 is attached thereto. Various means may be provided for effecting, these operations. In the disclosed embodiment, the tube 5 is continuously rotated axially on a lathe or other suitable'device and Fig. 3; The roll 9 may be journaled in a. block 20, slidably supported in a frame 21 and the rolls 9 and 19 may be journaled in'similar blocks 22 and 23 slidably supported .irr'the frame 24. The roll-carrying blocks 20, 22 and 23 may be respectively movable by screwmeans indicated at 25, 2 6 and 2'7 to facilitate the insertion of the tube 5 between the rolls. The frames 21 and 24 may be moved in unison along the tube by any suitable means. A fin guide 28 is preferably provided,'and as shown, may be fixed to the frame:

24. The end of the guide 28 is-disposed adjaceiit the tube 5 between the knurling roll 9 and the lead and tension roll 8, and embraces the fin 7 in a slot 29. I

The lead and tension roll 8 is preferably constructed to provide a peripheral groove 13 for the reception of the fin 7, at least a portion of this peripheral'groove being disposed at an angle to the normal plane of the fin. As best shown in Fig. 4, this may be accomplished by forming theroll 8 in two parts 31 and 32 having parallel complementary frusto conical end surfaces. These surfaces. are sufliciently separated to accommodate the fin 7 therebetween, but the angular disposition of the fin groove results in a firm frictional engagement between the fin '7 and the roll 8 whereby the inner edge of the fin is tightly pressed on thetube surface and the fin is maintained under; sufficient tension to ensure tight winding on the tube.

The tube supporting roll 19 may comprise two spaced parts forming a peripheral groove 33 therebetween, as shown 'in Fig. 5. The groove 33 in this roll merely acts to accommodate the fin 7 so that the peripheral surfaces of the roll may engage and support the tube 5. y

The knurling roll 9 is provided on its peripheral surface with a plurality of teeth or serrations 14 which extend substantially at right angles to the,

plane of rotation of this roll. Theroll 9 is firmly pressed against the surface of the tube 5 and thus, as the tube rotates, forms surface protrusions or knurl marks 6 on the tube. The knurl marks or protrusions 6 are generally ridge-like in character and extend in a direction generally longitudinally of the tube. The knurling roll 9 is preferably of sufficient width so that in its movement along the tube 5, it forms knurl marks or protrusions along substantially the entire surface of the tube, although it is suflicient for the purposes of the invention that the knurl marks cover the path of the fin 7.x

As showniin Figs. 1, 3, 4 and 5, the fin '7 used may be prefor n'edto a coil having an inner'd1-. ameter slightly greater than the outer diameter of the tube 5. This precoiling of the fin may be accomplished in any suitable manner, as for. ex ample, by the means disclosed in my copending application, Serial No. 463,193, filed October 29, 1929. With the precoiled fin in place on the tube 5, and the fin 7 inserted in the peripheral groove 13 of the lead roll 8, the groove 33 of the tube supporting roll 19 and the slot 29 of the guide 28, the

fin attaching operation is initiated by rotating the tube 5 and simultaneously advancing the rolls 8, 9 and 19 along the tube. The knurling roll 9 first engages the tube surface and forms the knurl marks or surface protrusions 6 thereon, and as the rotation of the tube continues, the lead roll 8 tightly winds the fin 7 on the previously knurled tube surface and presses the inner edge of them against this surface with sufficient force to cause the protrusions or knurl marks 6 to embed themtration of the protrusions into the fin edge pre- 36 vents movement of the fin longitudinally along the tube. The bending of the outer edge of the fin 7 as it passes through the angularly disposed groove 13 'of the lead and tension roll 8 serves not only to maintain the fin under tension during winding and press the finedge against the knurl marks 6, but also acts to stretch the portion of the fin metal adjacent its outer edge beyond the elastic limit of this metal therebysetting the fin in its curved or wound position, while the inner portions of the fin are elastically compressed to an extentshort of the elastic limit of the fin metal. The woundfin, after being subjected to this treatment, is permanently and tightly fixed to the tube, since. the elastically compressed inner portion thereof tends to expand between the set outerportion and the tube surface. This stretching of the outerfin metal beyond its elastic limit and an elastic compression of the inner fin metal during winding may be accomplished in other ways and in some cases, the relation between the fin width and the diameter to which it is bent in coiling it on the tube may be so'chosen as to accomplish thedasired result. The present invention embraces this method as well as that first described above.

It will be apparent that the improved finned tube of the invention may be formed by methods varying in somerespects from that described above. Thus, the-longitudinally extending protrusions or knurl marks 6 may be formed on the tube 5 before the fin winding operation is effected,.

As shown in Fig. 2, the smooth metallic tube 5 may be drawn through the opening in a die 15 having tooth or serration forming grooves 16 on the inner surface thereof. These grooves 16 form longitudinally extending ridge-like protrusions or knurl marks 6' on the tube surface, similar to the protrusions or knurl marks 6 formed by the knurling roll 9 of Figs. 3, 4 and 5.

After the protrusions or knurl marks '6' have been formed by the die 15, the precoiled fin '7 may be attached to the tube 5 bytightly winding the fin about the .tube and pressing the inner employed for this purpose. The application of out any weakening of the tube structure. The penetration of the ridge-like protrusions on the ihg roll 9' and a tube compressing the inner portion of the tube metal. In the appended claims, the terms protrusions" and "knurl marks" are used to denote any form of surface irregularities which produce extensions capable of at least partially embedding themselves into the edge surface of the fin.

I claim: Y 1. The method of securing a metallic helical edge of the fin against the protrusions 6' so that these protrusions bite into the fin edge. This operation may be effected in the manner described above'in connection with-Figs. 3, 4 and 5, a lead and tension roll,

the fin 7 to a tube having previously formed surface protrusions or knurl marks '6' thereon is shown in Fig. 1. fin to a metallic tube which comprises roughen- If desired, the fin may besimultaneously coiled irig the outer surface of the tube to produce surand wound on the tube, and apparatus for acface protrusions thereon and tightly winding 8. complishing this has been diagrammatically ilfin helically on the roughened surface of the lustrated in Fig. 6. v In this embodiment, the tube tube." 5-is rotated in the direction indicated by the arrow between a lead and tension roll 8', a knurlsupporting roll 19', carried by frames 21' and 24' which move longitudinally along the tube 5 as the winding operation progresses. The rolls 8', 9'

fin to a metallic tube which comprises forming a plurality of elongated surface protrusions extending substantially longitudinally of the tube and helically winding a fin on the tube over such extensions with sufficient force to embed the .sufllcient force to cause penetration of the knur marks on the tube into the inner'edge of the fin. 4. The method of securing a metallic helical fin to a metallic tube'which comprises forming on the tube surface a peripherally continuous suc- \1 cession of knurl marks presenting ridge-like propassing through the angularly disposed peripheral groove therein and puts the proper tension on the ribbon so that it will be adequately taut as it approaches the tube 5.

- In operation, the tube 5 is rotated as indicatc d,

the knurling roll 9' forms a plurality of knurl the-tube. tightly winding a fin edgewise on the marks or surface protrusions extending substanprotrusions or knurl marks on the tube penetrate the .inner edge of the groove of the lead and tension roll 8', inner portion of the fin metal is elastically compressed between the set outer fin metal and the tube surface thereby ensuring a permanently knurled tube surface with sufilcient force to cause penetration of the tube surface" knurl marks into the inner edge surface of the fin.

6. The method of securing a metallic helical fin to a metallic tube which comprises forming, a plurality of longitudinally extending ridge-like protrusions on a tube, passing the tube through a precoiled helical fin and progressively pressing the inner edge of the fin against the tube surface with suflicient force to cause penetration of the tube surface protrusions into the inner edge of the fin.

7'. The method *of securing a helical fin to a tube into the inner edge of the fin permanently tube The intimate contact between the fin edge and the tube surface caused by the tight winding and elastic compression of the fin produces an eflicient heat con-. ductive joint without the use of solder and withsurface protrusions into the inner edge of the fin. 8. The method of securing a metallic helical by the knurling method alone or by a combination of knurling the tube surface vand resiliently 2. The method of. securing a metallic helical fln to-a metallic tube which comprises roughening the outer surface of the tube to produce surface protrusions thereon, winding a fin helically on the roughened tube surface and maintaining 5 the fin under sufiicient tension during the winding operation to embed the tube protrusions into the inner edge 0! the fin. a

9. The method oi. scuring a metallic helical fln to a metallic tube which comprises forming on 10 the tube surface a peripherally continuous succession of knurl marks presenting ridge-like pro trusions extending substantially longitudinally of the tube, winding a fin edgewise on the tube over such protrusions and simultaneously maintain- I ing the fin under tension andimpressing the inner edge of the fin against the tube surface to cause penetration of the tube surface'protrusions into the inner edge of the fin.

EDWARD A. DEWALD. 

